It is important that milling cutters and boring tools with replaceable or indexable cutting chips or inserts are so constructed that the inserts are precisely positioned with respect to the axis of rotation, and hence on the body of the tool. Only precise positioning ensures that accurate circular cutting and plane or end cutting by the cutting edges of the cutter bits can be ensured. Milling or boring heads which are to cut sharply defined corners, and milling heads in which individual cutting chips are located along a spiral path, are usually so constructed that the body of the tool itself is formed with pocket-like recesses which define an engagement or seating surface for the cutting chips. These surfaces are delimited by precisely finished lateral surfaces to form abutments for a cutter bit secured to the respective seating or engagement surface.
It has been proposed to use apertured index elements or chips which are attached to the respective seating surface by a clamping bolt (see the referenced U.S. Pat. No. 4,283,163, Grafe et al). To ensure a snug fit, the clamping bolt has a radially projecting conical portion between the clamping head and the threaded part thereof. By slight lateral elastic deformation of the clamping bolt against the inner wall of the opening in the chip, which preferably is also conically formed and decreased inwardly in diameter. By suitable selection of the size and the direction of the relative offset of the axes of the threaded bore and the body of the tool and the bore or opening in the indexing chip, forces directed towards the engagement surface or seat can be predetermined. These forces press the chip against the engagement surface.
Closed seats for chips, for example of the type described in the referenced Bohnet et al., U.S. Pat. No. 5,049,011, are expensive to make, and hence, in use, costly. This is true particularly for milling cutters which have the chips arranged along spirals, so that, in effect, a spirally toothed tool is generated. The chips are placed along the circumference of the tool body in screw-like spiral cutter rows. The referenced Dotany U.S. Pat. No. 5,083,887 shows such a cutting tool.
To reduce the complexity and cost of manufacture of such tools, a preferred form has been proposed in which the precise engagement of the cutting insert on the surface is defined by a pin. This pin is fitted, in essentially radially or tangentially formed openings in the tool body, and has, if desired, a precisely machined engagement surface for the cutting insert.
Such pins, particularly in spirally toothed index insert milling cutters, cause problems with respect to cutting chip removal. Cutting chips can catch or wedge between the pin and the subsequent cutting insert. Difficulties also arise when inserts of a large corner radius are used, since it is difficult to provide an accurately axially defined abutment. The pin, to provide a suitable abutment and define a position, must extend over a comparatively long distance from the body in order to ensure a reliable engagement at larger corner radii. Pins which are used in spirally toothed tools must be fitted in the tool body, which may lead to weakening of the tool body due to the bores in which the pins are to be received. This weakening reduces the lifetime of the tool body itself.